#!/user/bin/python
def binary_search(list, item):
    low = 0
    high = len(list)-1
    while low <= high:
        mid = (low + high) / 2
        guess = list[mid]
        if guess == item:
            return mid
        if guess > item:
            high = mid -1
        else:
            low = mid + 1
    return None

my_list = [1,3,5,7,9]

print binary_search(my_list, 5)

